1. Field of Invention
This invention relates to amniotic membrane grafts especially usable in the repair of injured eyes. This invention also encompasses: a method for separating and preserving amniotic membrane for a graft; the graft that is created by such method; and methods of repairing eyes and other organs while using these grafts.
2. The Prior Art
Terminology:
An amniotic membrane has two major components: the basement membrane and stroma. The side of the amniotic membrane dominated by the basement membrane is referred to as the "basement membrane side". The side of the amniotic membrane dominated by the stroma is referred to as the "stroma side". An autograft is a tissue transplant from the same recipient. When used in subcutaneous tunnels, autografts of the amnion become a permanent structure. In contrast, allografts are replaced by hyaline-like material. An allograft is a tissue transplant to a recipient from a donor of another individual of the same species.
Previous Clinical Applications
The fetal membrane including amnion (amniotic membrane) and chorion has been used in surgeries documented as early as 1910 and has been reviewed by Trelford and Trelford-Sauder in 1979. See Trelford and Trelford-Sauder, The Amnion in Surgery, Past and Present, 134 AM J. OBSTET. GYNECOL 833 (1979). In the beginning, the fetal membrane was used by Davis in 1910 on burned and ulcerated skins with additional coverage of warm paraffin and dressing. In 1940, De Rotth used fetal membrane for ophthalmic reconstruction of symblepharon, and noted a success in one out of six cases. See De Rotth, Plastic Repair of Conjunctival Defects with Fetal Membranes, 23 ARCHIVES OF OPTHAMOLOGY 522 (1940). In 1952, Douglas thought chorion might be more useful for skin use. Massee and colleagues in 1962 used the fetal membrane in dogs to treat pelvic basins after total exenteration; however, the human trials proved disappointing.
The isolated amnion alone was first used by Brindeau in 1935 and Burger in 1937 as a graft in forming artificial vaginas. Between 1941 and 1948, Kubanyi used "live" amnion in patients with burns, traumatic skin wounds, and enterocutaneous fistula secondary to surgery for lysis of adhesions. The isolated amnion, with preservation in a technique termed "amnioplastin", was first reported by Chao and associates in 1940. Chao used amnioplastin for continual dural repair, peripheral nerve injuries, conjunctival graft and flexor and tendon repair. In the Russian literature, this technique was also used for fresh trauma by Pikin in 1942.
Although all reports were enthusiastic, mention of "amnioplastin" disappeared from the literature with no real explanation. No critical reports regarding isolated, non-living amnion with preservation were found for a thirty-year period. Furthermore, if there were failures of treatment during this time, they were not reported. This gap in research ended in 1972 with the research of Trelford and associates, cited above. Trelford, using isolated amnion with an early form of preparation, showed that the orientation with stromal side down provided more consistent "take." Robson and colleagues noted in 1972 that, when used in partial-thickness skin wounds, no "take" occurs, and the amnion peels off. In 1973 and later, Trelford and associates reported its use as a dressing on full-thickness skin wounds, to replace pelvic peritoneum, and to cover exposed deep surfaces in pedicle graft procedures, to treat non healing skin wounds in diabetic patients, as a graft over the surgical defect of total glossectomy, as a biological dressing in omphalocele, and in the prevention of meningocerebral adhesions following head injury.
Previous Methods of Preparation and Preservation:
All of the above-mentioned applications appeared to have used live tissues or tissue removed and preserved "lively" in a special solution before use. For example, de Rotth put the fetal membrane, amnion and chorion together without separation, in "tepid Locke solution", and one to fifteen hours after cesarean section the tissue was implanted to patients. Reports which appeared after 1980 refer to live amniotic membranes having been used (See 34 J. REPRODUCTIVE MED. 198 (1989) and 27 J. PEDIATRIC SURGERY 882 (1992)). For "amnioplastin", Chao and associates isolated the amnion, placed it in 70% alcohol, and then dried it in an oven prior to use. Robson and associates rinsed the membrane in a 0.025% NaOH solution and showed that it remained sterile up to six weeks when stored in saline containing penicillin at 4.degree. C. Trelford and associates found that amniotic membranes stored at 4.degree. C. in 0.5N saline to which polymyxin, ampicillin, gentamicin, and amphotericin B was added were sterile at the end of four hours and remained so for at least 48 hours.